1. Field of the Invention
The present invention relates to a vehicle running control system that sets a target inter-vehicle distance to a preceding vehicle to be shorter when the preceding vehicle is turning to the right or left than when the preceding vehicle is traveling straight ahead.
2. Description of the Related Art
Various running control systems have been proposed in which a traveling environment in front of a subject vehicle, such as a car, is detected by a front-environment recognition device mounted in the subject vehicle and includes a camera, a millimeter-wave radar, a laser radar, or the like and in which running of the subject vehicle is controlled on the basis of the detected traveling environment. In these running control systems, when a preceding vehicle, which is traveling ahead of the subject vehicle, is recognized as being in front of the vehicle by the front-environment recognition device, a target inter-vehicle distance is set on the basis of the speed of the subject vehicle or the preceding vehicle, and follow-up running control is performed while maintaining the target inter-vehicle distance. In contrast, when no preceding vehicle is recognized as being in front of the subject vehicle, constant-speed running control is performed at a vehicle speed set by the driver beforehand (set vehicle speed).
In follow-up running control, when the preceding vehicle brakes and decelerates, the inter-vehicle distance between the subject vehicle and the preceding vehicle becomes shorter than the target inter-vehicle distance. Therefore, the subject vehicle is also decelerated by brake control so that the actual inter-vehicle distance returns to the target inter-vehicle distance. Hence, when the preceding vehicle is decelerated prior to making a right or left turn (hereinafter referred to as a right/left turn), the subject vehicle is also decelerated. After the preceding vehicle moves out of a traveling lane of the subject vehicle at a later time, the subject vehicle is accelerated.
The moving speed of the preceding vehicle, which is detected by the subject vehicle when the preceding vehicle is making a right/left turn, is determined from the vector in the straight traveling direction of the subject vehicle. Therefore, the moving speed is lower than the speed in the traveling direction of the preceding vehicle. For this reason, in a running control system that performs brake control according to the inter-vehicle distance and the relative speed, even when the preceding vehicle is making a right/left turn, the target inter-vehicle distance is set on the basis of the vehicle speed detected in the vector in the traveling direction of the subject vehicle. When the actual inter-vehicle distance becomes shorter than the target inter-vehicle distance, brake control is carried out.
Accordingly, when the preceding vehicle makes a right/left turn during conventional follow-up running control, braking is performed earlier than the driver recognizes the right/left turn of the preceding vehicle and presses the brake pedal. Further, when the subject vehicle comes close to the preceding vehicle during conventional follow-up running control, an excessive brake force is applied.
In general, when the driver recognizes a preceding vehicle making a right/left turn, the driver estimates the time at which the preceding vehicle will move out of the traveling lane of the subject vehicle, performs braking in accordance with the time, and tries to pass the preceding vehicle while reducing the speed of the subject vehicle to a predetermined speed.
In contrast, in the above-described brake control method of the related art, the speed of the preceding vehicle that is traveling straight ahead and the speed of the preceding vehicle detected as the vector in the traveling direction of the subject vehicle at the right/left turn are processed as the same parameter. Therefore, brake control is exerted in response to the preceding vehicle that is making the right/left turn, earlier than the brake timing intended by the driver, and a brake force that is stronger than expected is applied. This makes the driver feel discomfort. Moreover, since there is a tendency for deceleration to be excessive, acceleration driving is delayed after the subject vehicle has passed the preceding vehicle.
For example, Japanese Unexamined Patent Application Publication No. 2000-57499 discloses a technique as a measure against the above-described problems. In this technique, a traveling path and a speed of a preceding vehicle are calculated on the basis of information about the distance between the preceding vehicle and a subject vehicle and information about the lateral position of the preceding vehicle. From the calculation result, a speed vector of the preceding vehicle is calculated. When the speed vector greatly changes in the traveling direction and the vehicle speed greatly changes, it is determined that the preceding vehicle is making a right/left turn.
According to the technique disclosed in this publication, it is possible to recognize a right/left turn of the preceding vehicle early in follow-up running control. When the right/left turn of the preceding vehicle is recognized, smooth running control can be performed without excessive brake control.
Unfortunately, it is difficult for the above-described technique to cope with a case in which the preceding vehicle further decelerates or stops during the right/left turn.
For example, when the preceding vehicle is making a right/left turn and encounters a pedestrian in the turning direction, the driver of the preceding vehicle further reduces the vehicle speed or stops the preceding vehicle, and then waits until the pedestrian has completely crossed the road. In this case, the rear of the preceding vehicle may stay in the traveling lane of the subject vehicle.
In this situation, the driver of the subject vehicle may desire to further decelerate the subject vehicle. However, since control is performed to uniformly reduce the brake force in the above-described technique, it is difficult to meet the driver's desire.